A problem common to most coal gasification and liquefaction processes is the lack of reliable, long-life pressure-letdown valves. Such systems must accommodate gas-solid and solid-liquid-gas mixtures at temperatures up to 900.degree. C. and pressures up to 20 MPa. Commercial development of such advanced fuel processes requires reliable, low-maintenance letdown systems. The standard approach to pressure letdown is to throttle the flow by reducing the flow area in a throated control valve. Unfortunately, high velocities in the valve throat combine with the abrasive solids content of typical coal-derived slurries resulting in excessive valve wear, lack of controllability, and short lifetimes. Attempts to use advanced materials that are more durable under such conditions have met with limited success.
A similar problem is encounted in control of a continuous flow ash lockhopper. The application (NASA NPO-16985-1-CU) titled "Energy Efficient Continuous Flow Ash Lockhopper" filed by Earl R. Collins, Jr., Jerry W. Suitor and David Dubis discloses a system shown here in FIG. 1 that employs a fluidics flow control chamber top allow ash from a lockhopper at the bottom of a coal slurry reactor to pass through under the force of gravity while preventing a flow of reactor gases to pass through with the ash by maintaining the fluid pressure in the chamber equal to or slightly higher than the internal reactor gas pressure. Consequently, for preventing the flow of reactor gases, while permitting the free gravitational flow of ash to a pressure letdown device, the control port of the chamber is designed for specified conditions, and a valve is operated to control the pressure of the control fluid (e.g., steam) into the chamber. In order for the system to operate under varying conditions, such as a varying rate of flow of ash from the lockhopper into the pressure letdown device, the chamber is provided with a pivotal D-shaped throttling sector in the inlet passage of the control fluid to allow for independent adjustment of the volume and velocity of control fluid into the chamber, which is shown to be steam from a cooling water jacket around the ash lockhopper, but may be any suitable fluid from another source.
The control chamber operates to maintain a fluidic force balance between the chamber pressure and the reactor pressure using a pressure controller which compares the reactor pressure with the chamber pressure, and adjusts the pressure of the control fluid in the chamber. The chamber is configured as a shallow disk-like chamber having an internal side wall that is kidney shaped, and a height that is significantly smaller than the transverse dimensions of the chamber. The ash exit port in the bottom of the chamber is positioned at the center of the chamber, and the ash inlet port at the top end of the chamber is offset from the exit port. The control fluid enters through the side wall and passes across the inlet port in a direction toward the side wall at the small end of the kidney shaped chamber to direct the flow of ash toward the side wall which then deflects, thereby creating a vortex that passes around and then over the exit port. While some control fluid will exit with the ash, the pressure of the control fluid in the chamber is continuously controlled to equalize, or even exceed slightly, the pressure in the reactor, and thus prevent any flow of toxic gas out of the reactor vessel.